Modern lifestyles have famously made humans heavier, but, in one particular way, noticeably lighter weight than our hunter-gatherer ancestors: in the bones. Now a new study of the bones of hundreds of humans who lived during the past 33,000 years in Europe finds the rise of agriculture and a corresponding fall in mobility drove the change, rather than urbanization, nutrition or other factors.
The discovery is reported in the early edition of Proceedings of the National Academy of Sciences the week of May 18. It sheds light, researchers say, on a monumental change that has left modern humans susceptible to osteoporosis, a condition marked by brittle and thinning bones.
At the root of the finding, the researchers say, is the knowledge that putting bones under the "stress" of walking, lifting and running leads them to pack on more calcium and grow stronger.
"There was a lot of evidence that earlier humans had stronger bones and that weight-bearing exercise in modern humans prevents bone loss, but we didn't know whether the shift to weaker bones over the past 30,000 years or so was driven by the rise in agriculture, diet, urbanization, domestication of the horse or other lifestyle changes," says Christopher Ruff, Ph.D. , a professor of functional anatomy and evolution at the Johns Hopkins University School of Medicine.
"By analyzing many arm and leg bone samples from throughout that time span, we found that European humans' bones grew weaker gradually as they developed and adopted agriculture and settled down to a more sedentary lifestyle, and that moving into cities and other factors had little impact."
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